The Ins and Outs of Hydration


Submitted By

The National Technology Development Program (NTDP)

hydration image 1 logo

Mmmm, nothing like that first pull of hot water from your hydration pack, you know the one where the water has been absorbing heat through the hose draped across your shoulder, or later in the season when your water bottle has a little extra flavor, and you haven’t added anything to it?

You might be a hydration pack person, or you might be a water bottle person. The best hydration device is the one you’ll use!

Hydration 1

NTDP field researcher conducting hydration analysis on a firefighter’s urine sample.

We Know Hydration is Important – But Why?

You are about 60% water! The brain and heart are composed of 73% water, the lungs are about 83%, the skin is 64%, muscles and kidneys are 79%, and even your bones are 31% water.

So that’s your thinker, your ticker, your ability to breathe and regulate body temperature, your first line of defense, the muscles that carry you up the hill, your filter that removes waste products, and the framework that holds it all together. And let’s not forget about blood!

Your blood consists of about 55% plasma and 45% of blood cells. Of the 55% that is plasma, approximately 90% is WATER! In fact, body water loss during exercise can increase your heart rate, impair performance, and reduce your ability to sweat.

Hydration” refers to maintaining water balance. Water that leaves your body (mostly urine and sweat) is replaced with water put back into your body from food and drink consumed throughout the day.

How Much Do Wildland Firefighters Drink?

Wildland firefighters have an uphill battle showing up for each shift hydrated. No one wants to get out of their sleeping bag in the middle of the night to urinate. But showing up to a work shift under-hydrated will make it more difficult to maintain water balance throughout the shift.

Montana WPEM has coordinated multiple studies with cooperation from NTDP for nearly 25 years. These studies have included measurements of water turnover or balance [see references 1-5 below]. Using this information, 24-hour fluid needs for a wildland firefighter can range from 6 to 10 liters, while workshift fluid intake values have been recorded from 3 to 7.5 liters for a 15-hour work period, which is about 300 – 500 ml per hour [see reference 1 below].

Morning, Day, and Night:

Consider what you eat and drink to take care of yourself.

While you’re sleeping, your body is slowing losing water and using stored nutrients to help your body recover, all while not resupplying [references 2,4].

Hydration is essential. But you cannot drink (water or electrolyte) your way out of a heat injury! A case study from 2004 showed a wildland firefighter drank 6 liters of water (170 drinks from a CamelBak) before experiencing a heat injury around 1400 [reference 6].

For more information on heat injuries and how to mitigate those, please visit our blog post here:

It’s important to remember that no two bodies are alike. What one person needs may be very different from the person sitting next to them. Your body size, the environment you’re working in, the work intensity and duration, the clothing you’re wearing, all influence the amount of water you’ll need. It’s crucial to listen to the clues your body is providing related to your water balance.

Some products commonly consumed by wildland firefighters may also affect your ability to hydrate, and thereby, offload heat. This is something to consider on days off when diuretics (cause urination), like alcohol, may be consumed. Ergogenic aids (e.g., creatine, caffeine) also have a varied effect on hydration status.


NTDP Field Electrolyte Study 2019: Evaluating hydration status of wildland firefighters throughout their workshift on large incidents. This data will be used for improvements to the NWCG Supplemental Food and Drink Guidance.

When water balance is compromised, dehydration can occur. Use these symptoms to monitor yourself and your buddy:

  • Mouth feeling dry
  • Headache
  • Dizziness
  • Rapid heartbeat

“Urine should be a ‘wheat’ color. If your urine is dark, you have not consumed enough water (you are dehydrated), and your body is holding on to as much water as it can. Remember to drink fluids before, during, and after the work shift. If your urine is clear, you have consumed too much water, and your body is trying to get rid of the excess. Drinking too much water can create as many problems as failing to consume enough.”

-Heat Illness Basics for Wildland Firefighters NTDP Fire Tech Tip 2010

However, just like other indicators of dehydration, it may not occur until after you lose 1 to 2% of your body weight in water. Since it’s challenging to measure water loss in the field, listen to your thirst but monitor your sweat rate, the color of your urine, and how much you urinate. Studies have shown that wildland firefighters do maintain their water balance reasonably well during a shift, despite high temps and exertion.

Thirst is a protective mechanism that tells you to change your behavior in order to maintain water balance.

Drinking: Chug Chug Chug or Sip Sip Sip?

So what is the proper way to drink? It turns out, both sippers and chuggers are doing it right. Recent studies have shown that both strategies can support proper hydration depending on what type of work you are performing [references 7-9]. Also, a new lab study from the Montana WPEM looked at 2-hour treadmill tests (uphill grade with a 35-pound pack) in a heat chamber. Across four trials, participants drank either straight water or a carbohydrate-electrolyte source while drinking an hours’ worth of fluid either all at the beginning of the hour or in 22 small doses (one every 2 minutes or so). There were no differences in markers of water balance, sweat rate, core body temperature, or overall thermoregulation across the trials [reference 9].

A study by NTDP in 2006 looked at the use of standard water bottles and sipping hydration systems (with hydration reservoirs and a sipping tube) on hydration and work output during fire suppression [reference 10]. While there was no difference in hydration markers, subjects did report that they felt the water was “cooler” in the sipping system.

If you suspect you are dehydrated, moderate your activities to reduce exertion while drinking fluids and snacking to recover what you think you’ve lost in sweat.

Eating – How Does it Play into Hydration?

Salty Sweater? You know the guy or gal with all the white lines on their shirt after a shift? The salt content in sweat varies, but around 900 mg of sodium is lost per liter of sweat. (That’s about one of your quart canteens full of sweat.)

Eating every 90 minutes is ideal for maintaining energy levels and hydration status. It doesn’t have to be a large meal, just something with some carbs and sodium to help with fluid balance. Food helps water cross from our GI tract into our bloodstream.

Listen to your body and take care of yourself. Fluid and nutrient intake help to ensure safety and performance on the fireline.

hydration blog image 5 NTDP field researcher weighing food plate2

NTDP field researcher weighing a food plate to calculate the daily nutrient intake of a firefighter. This study helped support revisions in the new Large Incident Food Contract,  with help from the University of Idaho and Montana WPEM.

Numbers to Aim for   On Lighter Assignments: On Higher Intensity Assignments:
Breakfast 1000 Calories 1500 Calories
During the Workshift 1500 Calories (Split into 6-8 snacks/meals) 1500-2000 Calories (Split into 6-8 snacks/meals)
Dinner 1000 Calories 2000 Calories

Not a calorie counter? Understood. 

Here’s a breakdown:

Essentially, the average dinner plate from a caterer at fire camp provides around 1,000 calories. So you can be part of the “clean your plate club” and call it good on assignments that are mellow and ask for bigger helpings on more intense assignments. There’s also the salad bar options to add to the mix.

A study from the U.S. military found that when individuals consumed adequate food across a seven-day window, they were able to maintain body electrolyte levels when only drinking water [reference 11], while yet another recent study documented that the average wildland firefighter consumed a daily total of 6500 mg of sodium, 3800 mg of potassium, and 3700 calories [reference 12].

Wildland firefighters and Americans in general have high sodium diets. The FDA recommends only 2,300 for the general public. Sweating all day can require more salt though, so it is recommended to eat or drink something with salt in it every hour that you sweat (for example: half a sandwich, snack item, or sports drink).

Recommended Adequate Intake [reference 13]

Males Females
Sodium 2,300 mg per day 2,300 mg per day
Potassium 3,400 mg per day 2,600 mg per day

Fun Fact: 2,300 mg is roughly the size of a teaspoon of salt…

Water? Or Water Plus Something Else (Flavor, Electrolytes and Carbs)?

Who doesn’t love choking down water that’s warm enough to make tea with? Have you ever tried to add a splash of flavor to your water?  Lemon-lime or Grape perhaps?

A study by Colorado State University allowed individuals to controlled the taste of their water while exercising in the heat. Surprisingly enough, they reported that the addition of flavored water didn’t increase consumption. [reference 14]. So maybe you don’t drink more due to adding flavor, but maybe that splash of flavor helps you to not drink less. Beyond adding flavor to water, more and more, insulated water bottles are being used on the fireline in an attempt to keep drinking water from getting to “tea making” temperature.

OK, so here’s the big question: What should I be drinking?

It’s important to consider that for some lighter work shifts, carbohydrate and electrolyte replacement from commercial drinks may not be necessary. All the fluid you need could come from water. And all the electrolyte you need could come from consistent snacking/meals. However, under hotter conditions, when sweat rates can nearly double, this is when the added electrolyte may be prudent. When work rates are higher than normal on more aggressive work shifts, this is when added carbohydrate may be practical.

Sports beverages during and after the shift can help maintain and replenish lost electrolytes as well as jump-start muscle glycogen (energy) stores to refurb for the next shift.

Current recommendations for sports beverages (NWCG Supplemental Food Guide):

Per 8 Oz Serving:

  • Carbohydrate: 9-19 g
  • Sodium: 120-240 mg

*Take note that many sports beverages provided at fire camp are 2 servings per bottle.

Other Recommendations:

  • Less than 95 calories per 8 oz. serving
  • No carbonation or other ingredients such as caffeine or other ergogenic aids.

What’s the Deal with Energy Drinks?

“Energy drinks should be avoided before, during, and after strenuous activities, until such time that proper safety and efficacy data are available. Some of the deaths allegedly due to energy drinks have occurred when a person consumed energy drinks before, during, and/or after performing strenuous activities.”

Statement by: U.S. Navy’s Nutritional and Ergogenic Supplements Guide and endorsed by the American College of Sports Medicine

Continued monitoring of adverse events related to energy drink consumption is needed to fully understand the rate, severity, and nature of reactions to these products. [reference 15].

Key Takeaways

  • Hydration helps offload heat (when sweating), but it will not prevent heat-related illnesses. Fluid balance is the goal.
  • Sipper or Chugger: If you sweat one quart, you need to put it back. The critical thing is to drink!
  • Food is a good source of electrolytes and carbohydrates. Don’t like to eat heavy when you’re out in the heat? Ensure that you’re at least eating frequent, small amounts throughout the day to keep yourself balanced.


For a deeper dive check out the following reports used to write this, or check out the NTDP webpage at:

  1. Cuddy, J.S., et al., Effects of an electrolyte additive on hydration and drinking behavior during wildfire suppression. Wilderness Environ Med, 2008. 19(3): p. 172-80.
  2. Cuddy, J.S., et al., Work patterns dictate energy demands and thermal strain during wildland firefighting. Wilderness Environ Med, 2015. 26(2): p. 221-6.
  3. Montain, S.J., et al., Efficacy of eat-on-move ration for sustaining physical activity, reaction time, and mood. Med Sci Sports Exerc, 2008. 40(11): p. 1970-6.
  4. Ruby, B.C., et al., Water turnover and changes in body composition during arduous wildfire suppression. Med Sci Sports Exerc, 2003. 35(10): p. 1760-5.
  5. Ruby, B.C., et al., Total energy expenditure during arduous wildfire suppression. Med Sci Sports Exerc, 2002. 34(6): p. 1048-54.
  6. Cuddy, J.S. and B.C. Ruby, High work output combined with high ambient temperatures caused heat exhaustion in a wildland firefighter despite high fluid intake. Wilderness Environ Med, 2011. 22(2): p. 122-5.
  7. Jones, E.J., et al., Effects of metered versus bolus water consumption on urine production and rehydration. Int J Sport Nutr Exerc Metab, 2010. 20(2): p. 139-44.
  8. Seery, S. and P. Jakeman, A metered intake of milk following exercise and thermal dehydration restores whole-body net fluid balance better than a carbohydrate-electrolyte solution or water in healthy young men. Br J Nutr, 2016. 116(6): p. 1013-21.
  10. Domitrovich, J. and B. Sharkey, Hydration Strategies for Firefighters. USDA Forest Service – NTDP Fire Tech Tip, 2008.
  11. Rose, M.S., et al., Acceptability and effect of carbohydrate-electrolyte solutions on electrolyte homeostasis during field training. Mil Med, 1991. 156(9): p. 494-6.
  12. Marks, A.N., et al., Total Energy Intake and Self-Selected Macronutrient Distribution During Wildland Fire Suppression. Wilderness Environ Med, 2020.
  13. National Academies of Sciences, E. and Medicine, Dietary Reference Intakes for Sodium and Potassium, ed. V.A. Stallings, M. Harrison, and M. Oria. 2019, Washington, DC: The National Academies Press. 594.
  14. Deming, N.J., et al., Self-selected fluid volume and flavor strength does not alter fluid intake, body mass loss, or physiological strain during moderate-intensity exercise in the heat. J Therm Biol, 2020. 89: p. 102575.
  15. Higgins, J.P., et al., Energy Drinks: A Contemporary Issues Paper. Current Sports Medicine Reports, 2018. 17(2): p. 65-72.

2 thoughts on “The Ins and Outs of Hydration

  1. Great article and important concept to reinforce. Firefighters perform at levels comparable to triathletes and need food – hyration levels to match!

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